Printed circuit board with substrate-integrated waveguide transition

ABSTRACT

In described examples, an integrated waveguide transition includes a substrate with a waveguide side and an opposing waveguide termination side. A first layer of metal covers a portion of the waveguide side, a second layer of metal is separated from the first layer of metal by a first layer of dielectric, and a third layer of metal covers a portion of the waveguide termination side and is separated from the second layer of metal by a second layer of dielectric. A substrate waveguide perpendicular to a plane of the substrate extends from the waveguide side to the waveguide termination side; and a length and a width of the substrate waveguide is defined by a fence of ground-stitching vias that short the first layer of metal and the second layer of metal to a plate of the third layer of metal that forms a back short.

This application is a continuation of U.S. patent application Ser. No.15/859,393, filed Dec. 30, 2017, the contents of which is hereinincorporated by reference in its entirety.

TECHNICAL FIELD

This disclosure relates generally to substrates that couple towaveguides, and more particularly to substrates such as printed circuitboards with a planar transmission line that couples to a waveguide.

BACKGROUND

High frequency (HF) integrated circuits (ICs) generate millimeter-wave(MMW) signals such as those used for automotive radar (from 76 GHz to 81GHz). Planar transmission lines on a substrate, such as a printedcircuit board (PCB), carry the MMW signal from one location on the PCBto another location. For example, a planar transmission line may carry aMMW signal from one MMW IC to another IC on the PCB, from a MMW IC to aradiating element or antenna, or from a MMW IC to a waveguide transitionbuilt into the PCB (a PCB waveguide transition). The PCB waveguidetransition couples the MMW signals from the planar transmission line onthe PCB into an external waveguide. Alternatively, the PCB waveguidetransition can couple an incoming MMW signal from an external waveguideonto the planar transmission line on the PCB.

PCBs are formed of dielectric materials and layers of conductive metalseparated by dielectric layers. A PCB waveguide transition is formed byetching a PCB waveguide through the PCB, coating the sidewalls of thePCB waveguide with a conductive material, attaching a waveguidetermination to one end of the PCB waveguide, and attaching a probe tothe end of the planar transmission line on the PCB. The probe ispositioned in the PCB waveguide to couple the MMW signal from a planartransmission line on the PCB to the external waveguide. PCB waveguidetransitions require complex manufacturing including: substrate etching;sidewall plating; and manual probe positioning and attachment. Theseprocesses are not compatible with high volume and low cost PCBmanufacturing.

SUMMARY

In described examples, an integrated waveguide transition includes asubstrate with a waveguide side and an opposing waveguide terminationside. A first layer of metal covers a portion of the waveguide side; asecond layer of metal separated from the first layer of metal by a firstlayer of dielectric; a third layer of metal covering a portion of thewaveguide termination side and separated from the second layer of metalby a second layer of dielectric; a substrate waveguide perpendicular toa plane of the substrate and extending from the waveguide side to thewaveguide termination side of the substrate; and a length and a width ofa cross section of the substrate waveguide defined by a fence ofground-stitching vias that short the first layer of metal and the secondlayer of metal to a plate of the third layer of metal that forms a backshort of the substrate waveguide.

In additional described examples, a packaged integrated circuitincludes: a substrate including a substrate-integrated waveguidetransition; a millimeter wave integrated circuit (IC) mounted on thesubstrate; and a waveguide mounting shim coupled to the substrate. Themillimeter wave IC and the substrate are in the packaged integratedcircuit; and the waveguide mounting shim is external to the packagedintegrated circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a prospective view of a substrate such as a printed circuitboard (PCB) with a substrate-integrated waveguide transition.

FIGS. 1B-1E are cross sectional views through the substrate in FIG. 1A.

FIGS. 2A-2C are top down views of the substrate-integrated waveguidetransition with different probes.

FIG. 3 is a cross section of system with two printed circuit boards thatexchange millimeter wave signals through waveguides.

FIG. 4 is a packaged integrated circuit that contains a millimeter waveintegrated circuit chip mounted on a substrate such as a printed circuitboard with a substrate-integrated waveguide transition.

FIG. 5 is a prospective view of two microwave horn antennas mounted onwaveguides attached to a substrate with substrate-integrated waveguidetransitions.

DETAILED DESCRIPTION

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts, unless otherwise indicated. The figuresare not necessarily drawn to scale.

As is further described herein below, certain structures and surfacesare described as “parallel” to one another. For purposes of thisdisclosure, two elements are “parallel” when the elements are intendedto lie in planes that, when extended, will not meet. However, the termparallel as used herein also includes surfaces that may slightly deviatein direction due to manufacturing tolerances. If the two surfacesgenerally lie in planes that are spaced apart and which would notintersect when extended infinitely if the surfaces were made withoutthese manufacturing deviations, these surfaces are also parallel.

As is further described hereinbelow, certain structures and surfaces aredescribed as “perpendicular” to one another. For purposes of thisdisclosure, two elements are “perpendicular” when the elements areintended to form a 90-degree angle at their intersection. However, theterm “perpendicular” as used herein also includes intersections that mayslightly deviate from 90 degrees due to manufacturing tolerances.

As is further described hereinbelow, certain structures and surfaces aredescribed as “coplanar” with one another. For purposes of thisdisclosure, two elements are “coplanar” when the elements are formed inthe same horizontal layer of material. However, the term “coplanar” asused herein also includes elements that may slightly deviate from beingexactly in the same plane due to manufacturing tolerances.

In the arrangements, a substrate-integrated waveguide transition (SIWT)is formed with a back short to provide a transition from a planarwaveguide on a substrate to a waveguide mounted to and extending awayfrom the substrate. The SIWT directs the millimeter wave signal in onedirection and terminates the signal in another direction. In an example,the substrate can be a printed circuit board (PCB). Other substrates foruse with electrical assembly are also useful with the arrangements.

The MMW frequency range is from 30 GHz to 300 GHz. An integratedwaveguide transition design cannot support the whole MMW frequencyrange. The waveguide transition design can be modified (dimensions,board stack up, etc.) to support a given frequency range within thisband. In an example, 71 GHz-86 GHz band is the operating frequency rangeof the SIWT that covers the frequency range used for automotive radars.The SIWT design can be modified to support different frequency bands,such as 57 GHz to 64 GHz, for example.

FIG. 1A illustrates a substrate 100 with a substrate-integratedwaveguide transition (SIWT) 101. In an example, the substrate is aprinted circuit board (PCB). The SIWT 101 couples a millimeter-wave(MMW) signal from a grounded coplanar waveguide (GCPW) 103, which is atransmission line, on the substrate 100 to an external rectangularwaveguide 132 (not visible in FIG. 1A, see 132 in FIG. 1C). The externalrectangular waveguide 132 attaches to a waveguide mounting shim 130 onthe SIWT 101. Although a rectangular shaped waveguide is used forillustration, any type of hollow or dielectric filled waveguide, such asa circular waveguide, can also be used and these modifications formalternative arrangements.

The waveguide side of the substrate 100 is defined to be the side of thesubstrate 100 to which the external waveguide (132 in FIG. 1C) isattached. The waveguide termination side of the substrate 100 is theopposing side of the substrate 100 and is the side of the substrate 100that forms the waveguide back short. The waveguide back short is neededto terminate the SIWT 101 in one direction and to direct the MMW signalsin the other direction and into the external waveguide 132 (see FIG.1C).

In this example, the substrate 100, a PCB, includes three layers ofmetal spaced from one another by dielectric material. A first layer ofmetal 104 covers a portion of the waveguide side of the PCB. A secondlayer of metal 106 is electrically isolated from the first layer ofmetal 104 by a first dielectric 110. The second layer of metal 106 formsa ground plane for the GCPW 103. A third layer of metal 108 iselectrically isolated from the second layer of metal 106 by a seconddielectric 112. The thickness of the second layer of dielectric 112 isapproximately equal to ¼+/−5% of the wavelength at center operatingfrequency. The third layer of metal 108 covers a portion of thewaveguide termination side of the PCB and forms the back short. Thethree layers of metal 104, 106, and 108 form parallel planes. Inalternative arrangements, more or fewer layers of metal can be used.

The length and width of a cross section of the SIWT are defined by afence of ground-shorting vias 122. Vias 122 connect the first layer ofmetal 104 and the second layer of metal 106 to the plate of third layermetal 108 on the waveguide termination side of the PCB. The plate ofthird layer metal 108 forms the substrate-integrated back short for theSIWT.

The SIWT 101 includes a first substrate waveguide opening 114 in thefirst layer of metal 104, a second substrate waveguide opening 116 inthe second layer of metal 106, and the fence of ground-stitching vias122 adjacent to and surrounding the perimeter of the first 114 andsecond 116 waveguide openings. The first and second substrate waveguideopenings, 114 and 116, are aligned and are separated from each other bythe first dielectric layer 110. The ground stitching vias 122 areperpendicular to the three layers of metal 104, 106, and 108 and shortthe first 104 and second 106 layers of metal to a plate of the thirdlayer of metal 108. The length and width of the ground-stitching viafence including ground-stitching vias 122 define the length and width ofa cross section of the SIWT. The length of the SIWT waveguide is definedby the height of the ground stitching vias 122.

The spacing from one ground stitching via 122 to an adjacent groundstitching via 122 is less than about ¼ of the center operatingwavelength of the SIWT. The spacing of third metal layer 108 from secondmetal layer 106 is equal to about ¼+/−5% of the center operatingwavelength of the SIWT.

The SIWT 101 is manufactured using standard PCB manufacturing methods.No additional post processing steps are required. An external waveguidemounting shim 530 (see FIG. 5 and the accompanying descriptionhereinbelow) is later attached to the PCB 500 to provide support for anexternal waveguide 532.

The length and width of the SIWT openings 114 and 116, and the lengthand width of the ground-stitching via fence of ground stitching vias122, depend upon the central operating frequency of the MMW signals ofinterest and upon the properties of PCB materials. The length and widthof the SIWT openings, 114 and 116 are optimized to achieve the bestimpedance matching and minimum insertion loss when coupling the MMWsignal from the GCPW 103 on the PCB 100 to the external waveguide (see132 FIG. 1C). Impedance matching with a reflection coefficient of lessthan −10 dB and with an insertion loss of less than 1 dB is desired.

The optimum dimensions of the SIWT openings, 114 and 116, also dependupon the dielectric constants and the thicknesses of the firstdielectric 110 and the second dielectric 112. Substrates such as PCBswith SIWTs 101 are selected to have dielectric layers 110 and 112 withlow attenuation of the MMW signals of interest. Dielectric material witha dissipation factor of less than 0.01 is desired. However, inalternative arrangements where the opening dimensions are not exactlyoptimum, the SIWT 101 will couple MMW signals to an external waveguide,even if performance of the device is not fully optimized.

FIG. 1B is a cross section taken perpendicularly through the groundedcoplanar waveguide (GCPW) 103, that is, taken along dashed line 1B-1B(FIG. 1A). The GCPW 103 carries MMW signals across the substrate 100.The GCPW 103 includes a signal lead 120 formed in the first metal layer104 plus first ground plane plates also formed in first layer of metal104. One first ground plane plate lays adjacent to each side of thesignal lead 120 separated from the signal lead 120 by a gap filled withdielectric 110. The first ground plane and the signal lead 120 of thecoplanar transmission line are coplanar and are both formed in firstmetal layer 104.

A second ground plane is formed in second metal layer 106. The secondmetal layer 106 is electrically isolated from the signal lead 120 andthe first ground plane plates by first dielectric layer 110. Electricfield lines 126 initiate on the signal lead 120 and terminate on thefirst and second ground planes (see FIG. 1B).

FIG. 1C is a cross section along dashed line, 1C-1C (FIG. 1A), throughthe middle of the width of the SIWT 101, through the middle of the widthof the probe 118 that terminates the signal lead 120, and lengthwisethrough the signal lead 120 of the GCPW 103. Also shown is a crosssectional view through an external waveguide 132, and waveguide mountingshim 130, mounted on the SIWT 101.

The external waveguide 132 is mounted on a waveguide mounting shim 130that is mounted on the SIWT 101 and substrate 100. As used herein, ashim is a mechanical spacer to provide a desired spacing between twoelements. Shim 130 provides a desired spacing between elements. A slotetched into the mounting shim 130 provides an air gap 129 thatelectrically isolates the signal lead 120 from the waveguide mountingshim 130. The external waveguide 132; the waveguide mounting shim 130;the three layers of metal 104, 106, and 108; and the ground-stitchingvias 122 are coupled to ground.

The probe 118 portion of the signal lead 120 extends between about 10%and 20% into the opening of SIWT 101. The location, size, and shape ofthe probe 118 can be chosen to tune the resonant frequency and increasethe bandwidth of the SIWT 101. The location, size, and shape of theprobe 118 can be optimized to achieve optimum or increased coupling ofthe MMW signal from the GCPW 103 to the external waveguide 132. However,if these characteristics are not optimized, the arrangements will stillcouple the MMW signals from the GCPW 103 to the SIWT 101 and to theexternal waveguide 132, even if the overall performance is less thanoptimal.

FIG. 1D is a cross section along dashed line, 1D-1D, (FIG. 1A) throughthe width of the SIWT 101 adjacent to the probe 118. The cross sectionin FIG. 1D is also through ground stitching vias 122 adjacent to andsurrounding the perimeter of the substrate waveguide openings 114 and116. The shorter dimension 134 of the cross section of the substratewaveguide openings 114 and 116 and shorter dimension 136 of theground-stitching via fence of the ground vias 122 determines the widthof the substrate waveguide in the cross section.

FIG. 1E is a cross section along dashed line 1E-1E, in FIG. 1A throughthe length of the SIWT 101 adjacent to the probe 118. The cross sectionis also through ground stitching vias 122 that form a fence adjacent toand surrounding the perimeter of substrate waveguide openings 114 and116. The longer dimension 136 of substrate waveguide openings 114 and116 and longer dimension 140 of the ground-stitching via 122 fencedetermine the length of the substrate waveguide in the cross section.

FIG. 2A is a plan view of a substrate 200 including a SIWT 201.Substrate 200 can be a PCB, for example. Other substrates used inelectrical assembly can be used. In FIGS. 2A-2C, similar referencesnumerals are used for elements similar to those in FIGS. 1A-1E, forclarity. For example, SIWT 201 corresponds to SIWT 101. FIG. 2A shows aplan view of the SIWT 201 from the waveguide side of the substrate 200.In an example, the substrate is a PCB with built-in SIWT 201 coupled toa WR-12 waveguide (bandwidth of 71 GHz to 86 GHz) is used forillustration.

Dimensions are different for waveguides that operate at differentfrequencies and dimensions are different for substrates with differentsubstrate material properties. The width and length of the cross sectionof external WR-12 waveguide in this example is 1.55 millimeters (mm)×3.1mm. The width and length of the substrate waveguide opening 214 in metallayers one and two are 1.45 mm×1.9 mm. The width and length of thesubstrate waveguide that is defined by the width and length of theground-stitching via fence is 2 mm×2.45 mm. These example dimensions arefor a SIWT built in a Rogers Corp. RO4835 PCB substrate. Thesedimensions can be adjusted to form alternative arrangements for otherfrequency waveguides and for other substrates and for other PCBmaterials.

FIGS. 2A-2C show plan views of the SIWT 201 on the waveguide side ofsubstrate 200 to illustrate example probe 217, 218, 219 designs. Thewidth, length, size, shape, and positioning of the probe within the SIWTcan be optimized to achieve the broadest bandwidth for SIWT 201 and toachieve optimum impedance matching with minimum insertion loss into theexternal waveguide. Many other probe designs can be used in addition tothe ones shown. Note that even in arrangements where the probe positionand size is not fully optimized, the SIWT 201 will couple MMW signals tothe waveguide, even if overall system performance is not optimized.

FIG. 2A shows an oval shaped probe 218 terminating the end of the signallead 220. The center of the long side of the oval shaped probe 218 isattached to the end of the signal lead 220. The distance that the signallead 200 extends into the SIWT 201, and the dimensions and positioningof the oval shaped probe 218 in the openings of the SIWT 201 aredetermined by modeling and by trial and error to provide the bestcoupling for the MMW signal from the GCPW 103 to the external waveguide132 (see FIG. 1A).

FIG. 2B shows the signal lead 220 terminated with a trapezoidal or fanshaped probe 217. The short side of the trapezoidal or fan shaped probe217 is attached to the end of the signal lead 220. The distance that thesignal lead 220 extends into the opening of SIWT 201, and the dimensionsand positioning of the trapezoidal or fan shaped probe 217 in thesubstrate waveguide are determined by modeling and by trial and error toprovide the best coupling for the MMW signal from the GCPW 103 to theexternal waveguide 132 (see FIG. 1C).

FIG. 2C shows the end of the signal lead 220 terminated in the center ofthe long side of a T-shaped probe 219. The distance that the signal lead220 extends into the opening of SIWT 201 and the dimensions andpositioning of the T-shaped probe 219 in the substrate waveguide aredetermined by modeling and by trial and error to provide the bestcoupling for the MMW signal from the GCPW 103 to the external waveguide132 (see FIG. 1C).

FIG. 3 illustrates in a cross section a MMW circuit system with twosubstrates, for example two PCBs, 300 and 356. Each PCB has two SIWTs.Waveguides 332 and 352 attached between the SIWTs couple the two PCBs300 and 356 together. In FIG. 3, similar reference labels are used forsimilar elements shown in FIGS. 1A and 2A. For example, substrate 300 inFIG. 3 corresponds to substrate 100 in FIG. 1A and to substrate 200 FIG.2A.

SIWTs 301 and 305, in a first substrate 300, couple MMW signals fromplanar transmission lines on the first substrate 300 into externalwaveguides 332 and 352. First ends of the waveguides 332 and 352 aremounted on SIWTs 301 and 305 on substrate 300. The orientation of thewaveguides 332 and 352 is perpendicular to the plane of first substrate300. The MMW signals with the same frequency or different frequenciescan be generated by one or more MMW ICs mounted on the first substrate300.

Second ends of waveguides 332 and 352 are mounted on SIWTs 354 and 358on the second substrate 356. The second substrate 356 is arranged to beperpendicular to the waveguides 332 and 352 and is parallel to the firstsubstrate 300. SIWTs 354 and 358 in the second substrate 356 couple MMWsignals from external waveguides 332 and 352 onto planar transmissionlines on the second substrate 356. The MMW signals may be routed to MMWICs on the second substrate 356 for further processing. Alternatively,the second substrate can be a planar MMW antenna that broadcasts MMWsignals. Each of the SIWTs is bidirectional and can either receive MMWsignals from or transmit MMW signals into the waveguides 332 and 352.

FIG. 4 illustrates a packaged integrated circuit 464 using a substrate400, a PCB in this example, with a SIWT 401. A MMW IC 450 is mounted onPCB 400 with the SIWT 401. An external waveguide mounting shim 430 isattached to the PCB 400 and the SIWT 401. The PCB 400 and MMW IC 450 arethen housed in a protective package 460. The external waveguide mountingshim 430 is external to the package 460. Shim 430 provides a mountingsurface for an external waveguide (not shown in FIG. 4) and a desiredspacing from the PCB 400. The external waveguide mounted to the shim asis shown in FIG. 5 and is further described hereinbelow. Provision ismade (signals 462) to provide power and signals to the MMW IC 450. Thispackaged integrated circuit 464 can be connected to the externalwaveguide to send and/or receive MMW signals.

FIG. 5 illustrates a projection of a substrate 500 with two SIWTs (notvisible in FIG. 5). In this example 500, the substrate can be a PCB. Anexternal waveguide mounting shim 530 is attached to and partiallyoverlying the PCB 500 to enable external waveguides 532 to be mounted.Two external waveguides 532 are mounted on the waveguide mounting shim530. A MMW horn antenna 570 is attached to each external waveguide 532.MMW signals can be transmitted or received through the MMW horn antennas570. The SIWT couples (not visible in FIG. 5, see 101 in FIG. 1C forexample) the received MMW signals to coplanar waveguides (not visible inFIG. 5) on the PCB 500 as described hereinabove.

Substrates (such as PCBs, for example) with one or more substrateintegrated waveguide transitions (SIWTs) each with an integrated backshort can be manufactured using standard substrate manufacturingprocesses. No additional post process steps are required. Use of thearrangements significantly reduces cost and significantly increasesreliability of substrates with a built-in substrate waveguidetransition.

Modifications are possible in the described examples, and otheralternative arrangements are possible within the scope of the claims.

What is claimed is:
 1. An integrated waveguide transition, comprising: asubstrate with a waveguide side and an opposing waveguide terminationside; a first layer of metal covering a portion of the waveguide side; asecond layer of metal separated from the first layer of metal by a firstlayer of dielectric; a third layer of metal covering a portion of thewaveguide termination side and separated from the second layer of metalby a second layer of dielectric; a substrate waveguide perpendicular toa plane of the substrate and extending from the waveguide side to thewaveguide termination side of the substrate; and a length and a width ofa cross section of the substrate waveguide defined by a fence ofground-stitching vias that short the first layer of metal and the secondlayer of metal to a plate of the third layer of metal that forms a backshort of the substrate waveguide.
 2. The integrated waveguide transitionof claim 1, wherein a spacing between the ground-stitching vias is lessthan one-quarter of a center operating wavelength.
 3. The integratedwaveguide transition of claim 1, in which the substrate is a printedcircuit board (PCB), and a thickness of the second dielectric is aboutone-quarter plus or minus five percent of a center operating wavelength.4. The integrated waveguide transition of claim 1, in which the widthand length of a cross section of the substrate waveguide are equal, andthe substrate waveguide is circular.
 5. The integrated waveguidetransition of claim 1, in which the width and length of a cross sectionof the substrate waveguide are not equal, and the substrate waveguide isrectangular.
 6. The integrated waveguide transition of claim 1, in whichthe width of a cross section of the substrate waveguide is about 2millimeters and the length of the cross section of the substratewaveguide is about 2.45 millimeters.
 7. The integrated waveguidetransition of claim 1, further including: a first substrate waveguideopening with a first perimeter in the first layer of metal; a secondsubstrate waveguide opening with a second perimeter in the second layerof metal; and the second perimeter is aligned with the first perimeter.8. The integrated waveguide transition of claim 7, and furtherincluding: the fence of ground-stitching vias adjacent to andsurrounding the first and second perimeters; and the ground-stitchingvias short the first layer of metal and the second layer of metal to theplate.
 9. The integrated waveguide transition of claim 7, in which awidth of the first and second substrate waveguide openings are about1.45 mm and a length of the first and second substrate waveguideopenings are about 1.9 mm.
 10. The integrated waveguide transition ofclaim 7, in which an operating bandwidth of the integrated substratewaveguide transition is 71 to 86 GHz.
 11. An apparatus, comprising: asubstrate with a waveguide side and an opposing waveguide terminationside, and further including: a first layer of metal covering a portionof the waveguide side; a second layer of metal electrically isolatedfrom the first layer of metal by a first dielectric layer; a third layerof metal electrically isolated from the second layer of metal by asecond dielectric layer and covering a portion of the waveguidetermination side; and the first, second, and third layers of metal lyingin planes parallel with a plane of the substrate; a waveguideperpendicular to the plane of the substrate and extending from thewaveguide side of the substrate to the waveguide termination side of thesubstrate, the waveguide having a first waveguide opening with a firstperimeter in the first layer of metal, a second waveguide opening with asecond perimeter in the second layer of metal, a length and width of across section of the waveguide defined by a length and width of a fenceof ground-stitching vias adjacent to and surrounding the first andsecond perimeters, the ground-stitching vias shorting the first layer ofmetal and the second layer of metal to a plate of third layer metal; andthe plate of third layer metal covering an end of the waveguide on thewaveguide termination side of the substrate, and the plate forming aback short of the waveguide.
 12. The apparatus of claim 11, in which aspacing between the ground-stitching vias is less than one-quarter of acenter operating wavelength.
 13. The apparatus of claim 11, in which athickness of the second layer of dielectric is about one-quarter plus orminus five percent of a center of an operating wavelength.
 14. Theapparatus of claim 11, in which a reflection coefficient is less thanminus ten dB and an insertion loss is less than one dB.
 15. Theapparatus of claim 11, in which the width and length of a cross sectionof the waveguide are not equal, and the waveguide is rectangular. 16.The apparatus of claim 11, in which the waveguide is rectangular, andthe width of a cross section of the substrate waveguide is about 2 mmand the length of the cross section of the waveguide is about 2.45 mm.17. The apparatus of claim 11, in which a cross section of the waveguideis rectangular and a width of the first and second waveguide openings isabout 1.45 mm and a length of the first and second waveguide openings isabout 1.9 mm.
 18. A system, comprising: a first substrate with a firstsubstrate-integrated waveguide transition; a second substrate with asecond substrate-integrated PCB waveguide transition; and a waveguidecoupled between the first substrate-integrated waveguide transition andthe second substrate-integrated waveguide transition.
 19. The system ofclaim 18, in which the second substrate contains a planar MMW antenna.20. The system of claim 18, in which the first substrate and the secondsubstrate are printed circuit boards (PCBs).
 21. A packaged integratedcircuit, comprising: a substrate including a substrate-integratedwaveguide transition; a millimeter wave integrated circuit (IC) mountedon the substrate; a waveguide mounting shim coupled to the substrate;the millimeter wave IC and the substrate in the packaged integratedcircuit; and the waveguide mounting shim external to the packagedintegrated circuit.
 22. The packaged integrated circuit of claim 21, inwhich the substrate is a printed circuit board (PCB).